The bad systems, that hurt efficiency and/or reliability are:
EGR - GONE
AIR - GONE
HAC - DON'T HAVE IT ON MY '77
TP - STILL HAVE IT, I THINK IT'S GOOD TO NOT BACKFIRE OR HAVE THE ULTRA-RICH EFFECT FROM CLOSING THE THROTTLE PLATES UNDER HIGH VACUUM. I GUESS IT BURNS MORE FUEL BUT IT WILL MAKE THE EXHAUST SMELL BETTER
vac retard - GONE W/ '79-'80 DISSY

The good systems:
PCV - STILL HAVE IT
vac advance - MY '79-'80 DISSY IS VAC ADVANCE
Evap - STILL HAVE IT
Decel fuel cut - NOT SURE ABOUT THIS ONE
HIC - DO NOT HAVE IT SINCE I DON'T HAVE THE FITTING ON THE CARB BASE PLATE, BUT DON'T HAVE ANY ISSUES WITH HOT IDLE STUMBLING
Dissy vent - HAVE IT HOOKED UP CORRECTLY

...my opinion is that other than the EGR, ignition retard and air injection, the other stuff performs useful functions in maximizing performance and fuel economy under more different driving conditions. It is also electronic engine control. Simply disabling the EGR, retard and AI is sufficient and is a lot less work. It isn't worth the effort to remove it.

HAI is hot air intake. That's the preheat hose on the aircleaner snorkel on 73-newer Cruisers. W/ a stock exhaust manifold bolted to the bottom of the intake manifold, it is redundant. A useful accesory w/ headers, especially in cool climates.

I am actually planning on recreating my HAI shield and hose (missing when I got the truck) at some point, rather than pay SOR a bunch of money for a rusted out one. But since I have the stock exhaust manifold hooked up I'm probably fine for a little while, never have had a problem yet. I wonder how it's supposed to work with headers since the shield will have nothing to bolt to? I guess it just draws ambient air from near the header and that's close enough to help. Fluid heat riser helps too.